1. Field of the Invention
The present invention relates to a magnetic resonance imaging system which images a coronary artery.
2. Description of the Related Art
Although coronary artery angiography using a CT including multiple rows of detectors, as many as 64 rows or more, i.e., a so-called MDCT (multi-detector row CT), has recently become popular, this examination method poses problems, e.g., a relatively high radiation dose and the use of a contrast medium. In a similar method using magnetic resonance imaging (MRI), there is no need to consider a radiation dose and there is no need to use any contrast medium. In addition, since MRI allows to simultaneously perform examination on myocardial blood flow information and the like, demands have arisen for the development of coronary artery MRA (MR angiography) using MRI.
The current mainstream method is called the navigator echo method (see patent reference 2). This method operates as follows. The motion of the heart itself and motion caused by respiration mainly pose problems in obtaining the image information of the heart. With the speed of MRI at present, it is difficult to obtain a high-resolution image which allows estimation of a coronary artery in several tens of seconds. It is therefore necessary to remove the influences of these two motions.
In order to remove the influence of the motion of the heart of the two motions, this method generally acquires data only for several tens of msec in synchronism with an ECG (electrocardiogram). In order to remove the influence of the respiratory motion, the method acquires one-dimensional MR data from a rod-like portion perpendicular to the diaphragm immediately before the acquisition of the above data and acquires heart data only in the interval during which the position of the diaphragm which is obtained from the acquired data is located in a predetermined range.
As described above, the navigator echo method acquires data only when both a cardiac cycle and a respiratory cycle exist in a predetermined range, and hence is extremely low in data acquisition efficiency in terms of time. Although various techniques like those disclosed in patent references 1 and 3 have been proposed, any of the techniques has not yet solved the problem of low data acquisition efficiency in terms of time.
patent reference 1: Jpn. Pat. Appln. KOKAI Publication No. 2000-60820
patent reference 2: Jpn. Pat. Appln. KOKAI Publication No. 2004-57226
patent reference 3: International Publication WO00/06245 brochure